**Core Concept**
Non-cirrhotic portal hypertension (NCPH) is a condition characterized by increased pressure in the portal vein system without cirrhosis. The most common clinical manifestation of NCPH is related to the consequences of portal pressure elevation.

**Why the Correct Answer is Right**
Upper gastrointestinal bleeding is the most common presenting symptom of NCPH due to the formation of varices in the esophagus or stomach. As a result of portal hypertension, blood is diverted through collateral veins, leading to the formation of varices, which are prone to rupture and bleeding. This is often the initial presentation in patients with NCPH. The increased portal pressure is typically caused by non-cirrhotic causes such as portal vein thrombosis, schistosomiasis, or other conditions that lead to increased resistance to blood flow.

**Why Each Wrong Option is Incorrect**
**Option A:** Chronic liver failure is not a direct consequence of NCPH and is more commonly associated with cirrhosis.
**Option B:** Ascites may occur in NCPH but is not the most common presenting symptom; it is more commonly associated with cirrhosis.
**Option D:** Encephalopathy is not a typical presentation of NCPH, as it is more commonly associated with cirrhosis and hepatic encephalopathy.

**Clinical Pearl / High-Yield Fact**
In patients with NCPH, the presence of splenomegaly and thrombocytopenia can be a clue to the diagnosis, as these are common findings in this condition.

**✓ Correct Answer: C. Upper gastrointestinal bleeding**